Vehicle rearward monitoring system and vehicle rearward monitoring method

ABSTRACT

A vehicle rearward monitoring system configured to monitor an object located behind and above a truck, the vehicle rearward monitoring system including: an object detection unit installed in the truck and configured to detect the object located behind and above an upper end of a rear end of the truck; an object specifying unit configured to specify a position, a size and a velocity vector with respect to the truck of the object detected by the object detection unit; and a collision possibility determination unit configured to determine a possibility of collision of the truck with the object detected by the object detection unit from the position, the size and the velocity vector of the object specified by the object specifying unit, and make a driver of the truck recognize the possibility of collision when it is determined that there is the possibility of collision.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of Japanese PatentApplication No. 2022-046661, filed on Mar. 23, 2022, the contents ofwhich are incorporated by reference as if fully set forth herein intheir entirety.

TECHNICAL FIELD

The present disclosure relates to a vehicle rearward monitoring systemand a vehicle rearward monitoring method.

BACKGROUND ART

A system for vehicles that captures the periphery of a vehicle for thepurpose of preventing collision and displays it on the monitor at thedriver's seat by converting the captured image into a perspective imageas viewed from the upper side of the vehicle so that the driver canrecognize the hindrance around the vehicle is known (PTL 1). Inaddition, a technique of capturing the periphery of the vehicle with acamera with a wider field angle than typical cameras such as wide-anglecameras is also known (PTL 2).

CITATION LIST Patent Literature

-   -   PTL 1    -   Japanese Patent Application Laid-Open No. 2022-23870    -   PTL 2    -   Japanese Patent Application Laid-Open No. 2022-6844

SUMMARY OF INVENTION Technical Problem

The hindrance around the vehicle includes not only hindrance on theroad, but also structures located above the vehicle such as the roof andeaves of the garage. In addition, in the case where the building has atwo-story structure, the structures inside the building such as theceiling of the first floor and the floor of the second floor areprovided above the vehicle.

However, in the technique of displaying the perspective image disclosedin PTL 1, the height of the structures above the vehicle are unknowneven when they are shown in the perspective image, the driver cannotdetermine whether the vehicle can travel under the structure withoutcolliding it especially when the vehicle moves backward. In addition,also in the image captured with the wide-angle camera disclosed in PTL2, the height of the structure above the vehicle is unknown even when itis captured in the image, and consequently the driver cannot determinewhether there is a possibility of collision especially when the vehiclemoves backward.

To solve the above-described problems, an object of the presentdisclosure is to provide a vehicle rearward monitoring system with whichthe driver can determine the possibility of collision of the vehiclewith a structure behind and above the vehicle.

Solution to Problem

To achieve the above-mentioned object, a vehicle rearward monitoringsystem according to one aspect of the present disclosure is configuredto monitor an object located behind and above a vehicle, the vehiclerearward monitoring system including: an object detection unit installedin the vehicle and configured to detect the object located behind andabove an upper end of a rear end of the vehicle; an object specifyingunit configured to specify a position, a size and a velocity vector withrespect to the vehicle of the object detected by the object detectionunit; and a collision possibility determination unit configured todetermine a possibility of collision of the vehicle with the objectdetected by the object detection unit from the position, the size andthe velocity vector of the object specified by the object specifyingunit, and make a driver of the vehicle recognize the possibility ofcollision when it is determined that there is the possibility ofcollision.

A vehicle rearward monitoring method according to another aspect of thepresent disclosure is configured to monitor an object located behind andabove a vehicle, the vehicle rearward monitoring method including:detecting the object located behind and above an upper end of a rear endof the vehicle; specifying a position, a size and a velocity vector withrespect to the vehicle of the object detected by the detecting; anddetermining a possibility of collision of the vehicle with the objectdetected by the detecting from the position, the size and the velocityvector of the object specified by the specifying, and making a driver ofthe vehicle recognize the possibility of collision when it is determinedthat there is the possibility of collision.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide a vehiclerearward monitoring system with which the driver can determine thepossibility of collision of the vehicle with a structure behind andabove the vehicle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a truck including a rearward monitoring systemaccording to a first embodiment of the present disclosure;

FIG. 2 is a functional block diagram of the rearward monitoring systemaccording to the first embodiment;

FIG. 3 is a perspective view for describing a procedure of detecting anobject located behind and above a truck with the rearward monitoringsystem according to the first embodiment;

FIGS. 4A and 4B are diagrams for describing a procedure of detectingwith the rearward monitoring system according to the first embodiment anobject located behind and above a truck, FIG. 4A is a side view of FIG.3 in which a warehouse is illustrated in a sectional view, and FIG. 4Bis a plan view of FIG. 3A;

FIG. 5 is a schematic view of an image of a warehouse captured with awide-angle camera serving as an object detection unit in the stateillustrated in FIGS. 3 and 4 ;

FIG. 6 is a flow chart illustrating a procedure of a rearward monitoringmethod using the rearward monitoring system according to the firstembodiment;

FIG. 7 is a side view for describing a procedure of detecting an objectlocated behind and above a truck with a rearward monitoring systemaccording to a second embodiment, in which a warehouse is illustrated ina sectional view;

FIGS. 8A and 8B are schematic views of an image in which a pole iscaptured with an object detection unit in the rearward monitoring systemaccording to the second embodiment, FIG. 8A illustrates an upper cameraimage captured with an upper camera, and FIG. 8B illustrates a lowercamera image captured with a lower camera; and

FIG. 9A is a schematic view of an image converted to an upward image asviewed from the ground from the upper camera image illustrated in FIG.8A, and FIG. 9B is a schematic view of an image converted to an upwardimage as viewed from the ground from the upper camera image illustratedin FIG. 8B.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present disclosure are elaborated belowwith reference to the accompanying drawings. Here, as rearwardmonitoring system 1, the following describes an example of a system fordetecting an object behind and above cargo bed 107 of truck 100, whichis a vehicle provided with cargo bed 107 of a van-body type. Inaddition, in the following drawings, the X direction is the front-reardirection of truck 100, the Y direction is the vehicle width directionof truck 100, and the Z direction is the vertical direction.

First, with reference to FIG. 1 , an overview of the structure of truck100 according to a first embodiment is described. Truck 100 illustratedin FIG. 1 includes chassis 103, which is a structure for supporting theapparatuses making up truck 100, cab 105, which is a cab provided at thefront end of chassis 103, cargo bed 107 provided at chassis 103 on therear side of cab 105, and rearward monitoring system 1.

Next, a structure of rearward monitoring system 1 according to the firstembodiment is described in detail below with reference to FIGS. 1 to 5 .As illustrated in FIGS. 1 and 2 , rearward monitoring system 1 includesobject detection unit 3, object specifying unit 7, and collisionpossibility determination unit 9.

Object detection unit 3 is an apparatus for detecting objects behind andabove truck 100, i.e., objects behind and above cargo bed 107 in thiscase, and is installed in cargo bed 107 of truck 100. The phrase “detectobjects” as used herein means acquiring information required forspecifying the position and size of the object and the velocity vectorof the object with respect to truck 100. For example, an image-capturingdevice such as a monocular camera can specify the position, size andvelocity vector of the object from the captured image through publiclyknown image analyses such as edge extraction. As such, a monocularcamera can acquire an image as information required for specifying theobject, and is therefore included in object detection unit 3. Inaddition, an apparatus such as a clearance sonar that emits ultrasoundto the surroundings and detects returning ultrasound reflected by theobject is also included in object detection unit 3 because such anapparatus can specify the position, size and velocity vector of theobject from the time required for the returning and the returningdirection of the ultrasound.

Unlike clearance sonars, a monocular camera does not emit waves such asultrasound, which is advantageous because it does not cause erroneousdetection of objects due to waves hitting cargo bed 107. Further, in thecase where truck 100 is provided with a known rearward monitoring camerasuch as a wide-angle camera, the camera can be used also as objectdetection unit 3, which is also advantageous. On the other hand, aclearance sonar can directly detect the position of the object from thedetected ultrasound, which is advantageous because the accuracy of theobject detection is higher than that of the combination of the monocularcamera and the image analysis. In the following description, unlessotherwise noted, a case where a wide-angle camera, which is a monocularcamera, is used as object detection unit 3 is described as an example.

For example, as illustrated in FIGS. 3 and 4A, it is assumed that truck100 is about to move back in the X1 direction into warehouse 111 fromentrance 113. In addition, it is assumed that warehouse 111 has atwo-story structure, and second-floor floor 115, which is the ceiling ofthe first-floor part and the floor of the second-floor part, areprovided at the back surface of warehouse 111 in such a manner as toprotrude in the X2 direction from the position higher than the upper endof truck 100.

In this case, object detection unit 3, which is a wide-angle camera,captures an image including a portion behind and above the upper end ofthe rear end of cargo bed 107 of truck 100. More specifically, itcaptures an image that shows the rear end of cargo bed 107, upper frame113 a of entrance 113 of warehouse 111, and the second-floor floor 115in warehouse 111. The field angle and optical axis of the wide-anglecamera may be appropriately set in the range where an image of a portionbehind and above the rear end of cargo bed 107 of truck 100 can becaptured. FIG. 5 illustrates an example of captured image G. Image Gillustrated in FIG. 5 shows warehouse 111, entrance 113 of warehouse111, upper frame 113 a of entrance 113, and the second-floor floor 115in warehouse 111. Note that image G is an image captured by thewide-angle camera, and therefore a portion that is originally a straightline is shown in a circular distorted shape.

In addition, object detection unit 3 acquires information required forspecifying the object at a predetermined time interval. In the casewhere object detection unit 3 is a wide-angle camera, object detectionunit 3 repeatedly captures images at a predetermined time interval. Thereason for this is to acquire the velocity vector of the object withrespect to truck 100 from the variation of the position and size of thedetected object on the image. In addition, the installation position ofobject detection unit 3 may be selected as necessary as long as objectsbehind and above cargo bed 107 can be detected. FIG. 1 illustrates anexample in which it is installed at the upper end of the rear end ofcargo bed 107. Regarding the installation position of object detectionunit 3 in the vehicle width direction, it is preferably be located atthe center in the vehicle width direction because the left and rightregions where objects can be detected are approximately equal to eachother in the vehicle width direction.

Object specifying unit 7 illustrated in FIG. 2 is an apparatus forspecifying the position, size and velocity vector with respect to truck100 of the object detected by object detection unit 3, and is providedin cab 105, for example. More specifically, object specifying unit 7acquires information required for specifying the object from objectdetection unit 3, and specifies the position and size of the object andthe velocity vector of the object with respect to truck 100 from theacquired information.

In the case where object detection unit 3 is a wide-angle camera, objectspecifying unit 7 acquires image G captured by the wide-angle camerafrom object detection unit 3 as information required for specifying theobject. In the case where object detection unit 3 is a clearance sonar,object specifying unit 7 acquires the time taken for returning theemitted ultrasound, the returning direction and the like from objectdetection unit 3 as information required for specifying the object.

In the case where object detection unit 3 is a wide-angle camera, objectspecifying unit 7 specifies the position and size of the object and thevelocity vector of the object with respect to truck 100 through imageanalysis from image G captured by the wide-angle camera. Morespecifically, it is preferable to specify the position of the objectthrough extraction of the corners of the object in image G by using thevariation in brightness in the image and the like, i.e., so-called edgeextraction, because the position of the object can be easily specified.The size of the object, or in this case, the width in the Y directionand the height in the Z direction, may be calculated from the rangeoccupied by the image of the extracted object. The velocity vector ofthe object as used herein means the travelling direction and relativetravelling speed of the object with respect to truck 100. In the exampleillustrated in FIG. 5 , the speed of warehouse 111 is normally 0 becausewarehouse 111 itself does not move. It should be noted that in image Gcaptured by the wide-angle camera, the position and size of second-floorfloor 115 and upper frame 113 a in image G vary when truck 100 moves.For example, when truck 100 travels in the X1 direction as illustratedin FIGS. 3 and 4A, truck 100 approaches upper frame 113 a andsecond-floor floor 115, and therefore the sizes of the captured upperframe 113 a and second-floor floor 115 gradually increase when image Gis repeatedly captured at a predetermined time interval. That is, onimage G, upper frame 113 a and second-floor floor 115 appear to moverelative to truck 100 at a predetermined speed in the X2 direction.Therefore, object specifying unit 7 specifies, as a velocity vector, therelative travelling speed and the travelling direction from thevariation of the position of the extracted object in a plurality ofimages G captured at a predetermined time interval by object detectionunit 3, and the variation of the occupied range in image G.

In the case where object detection unit 3 is a clearance sonar, objectspecifying unit 7 may specify the position, size and velocity vector ofthe object from the time taken for returning the emitted ultrasound,i.e., the time from emission to detection of the ultrasound, and thereturning direction of the ultrasound.

Collision possibility determination unit 9 illustrated in FIG. 2 is anapparatus for determining the possibility of collision of truck 100 withthe object detected by object detection unit 3 from the position, sizeand velocity vector of the object specified by object specifying unit 7,and is provided in cab 105, for example. In the case where collisionpossibility determination unit 9 is also an apparatus that makes thedriver of truck 100 recognize the possibility of the collision when itis determined that there is a possibility of collision of truck 100 withthe object detected by object detection unit 3. Note that thepossibility of collision means a state where there is an object within arange of the traveling path that is anticipated from the currenttravelling direction of truck 100, not a state where the collisioncannot be avoided unless the driver immediately brakes. Examples of thecriterion for determining the possibility of collision of truck 100 withthe object are as follows.

First, collision possibility determination unit 9 determines whether thesize of the object specified by object specifying unit 7 is not smallerthan a predetermined size. When the size is smaller than thepredetermined size, collision possibility determination unit 9 does notdetermine the possibility of collision. The reason for this is that itis not necessary to determine the possibility of collision for thematters such as trash or dust floating in the air that cause no problemeven if they hit truck 100. The size not smaller than a predeterminedsize is a size which may possibly damage truck 100 when collided withtruck 100, for example.

Next, collision possibility determination unit 9 determines whether theobject specified by object specifying unit 7 will collide with truck100. More specifically, it determines whether the object specified byobject specifying unit 7 falls within region 23 surrounded by guide line21 when guide line 21 indicating the outer periphery in back view of therear end of cargo bed 107 of truck 100 illustrated in FIGS. 3 and 4A isextended rearward of truck 100. As a result, when it is determined thatit does not fall within region 23, it is determined that there is nopossibility of collision. The reason for this is that since region 23surrounded by guide line 21 is located inside the traveling path of thetravelling vehicle, there is no possibility of collision when the objectdoes not fall inside region 23. Note that region 23 surrounded by guideline 21 is set as follows. First, as illustrated in FIG. 3 , rearwardguide line 21 a, which is a type of guide line 21 with the samedimension and shape as those of guide line 21, is set at a location thatis on the rear side of guide line 21 and corresponds to the position ofguide line 21 when truck 100 moves back by a predetermined distance withthe current steering angle. The upper limit of the predetermineddistance is a distance corresponding to the upper limit distance of thedetection of object detection unit 3. Next, the corner of guide line 21and the corner of rearward guide line 21 a are connected to each otherwith line 21 b. The portion surrounded by guide line 21, rearward guideline 21 a, and line 21 b is region 23.

Note that guide line 21 need not have exactly the same size as the outerperiphery of the rear end of cargo bed 107 in back view. For example,width B4 of guide line 21 illustrated in FIG. 4B is the same as thewidth of cargo bed 107, while height B1 of guide line 21 illustrated inFIG. 4A is higher than height B3 of cargo bed 107. This is toaccommodate a case where the height of the rear end of cargo bed 107 istemporarily increased when truck 100 travels over a partially raisedportion such as step 121 on road surface 109 illustrated in FIG. 4A. Assuch, an example of height B1 may be a height corresponding to the rearend of cargo bed 107 when travelling over the highest possible step 121.In addition, the position of guide line 21 need not necessarilycompletely match the position of the rear end of cargo bed 107. Asillustrated in FIG. 4A, guide line 21 may be set at a position on therear side by a predetermined distance B2 from the rear end of cargo bed107. This is to accommodate the braking distance of a case where thedriver applies the brakes to avoid collision with an object located inregion 23 surrounded by guide line 21.

The position of rearward guide line 21 a differs depending on thetravelling direction of truck 100. In FIG. 3 , truck 100 is moving backto the X1 direction parallel to the X direction, which is the front-reardirection, and therefore the position of rearward guide line 21 a is onthe rear side of guide line 21 in the X direction. On the other hand,for example, in the case where truck 100 is moving back while turningleft or right, the position of rearward guide line 21 a is a positionshifted left or right from guide line 21. Line 21 b is also a curvedline, not a straight line when truck 100 is turning. The reason for thisis that region 23 is a range representing the traveling path of truck100. Note that whether truck 100 is turning can be acquired fromsteering angle sensor 11 illustrated in FIG. 2 .

Next, collision possibility determination unit 9 determines that thereis a possibility of collision when the velocity vector of the objectspecified by object specifying unit 7 is greater than the speed of truck100 and the directions of the velocity vectors of object and truck 100are opposite to each other. More specifically, it is determined thatthere is a possibility of collision when an object and truck 100 areapproaching each other. The reason for this is that it is determinedthat there is no possibility of collision when they are moving away fromeach other. In this manner, collision possibility determination unit 9determines that there is a possibility of collision when the detectedobject has a size equal to or greater than a predetermined size, fallswithin region 23, and approaches each other. Thus, the possibility ofcollision can be determined in accordance with the travelling state oftruck 100. Note that the speed of truck 100 can be acquired from speedsensor 13 as illustrated in FIG. 2 . The travelling direction of truck100 may be determined from the steering angle and the rotating directionof the wheels of truck 100.

When it is determined that there is a possibility of collision of truck100 with an object, collision possibility determination unit 9 makes thedriver of truck 100 recognize the possibility of the collision. Anexample of a specific means for recognition may be a means that notifiesthe possibility of collision with sound in the case where speaker 17illustrated in FIG. 2 is provided in cab 105. In addition, in the casewhere display unit 15 for displaying image G illustrated in FIG. 5 isprovided in cab 105, emphatic display 31 emphasizing upper frame 113 aof entrance 113 of warehouse 111, which is an object detected from imageG, may be displayed in a superimposed manner on image G displayed indisplay unit 15 as illustrated in FIG. 5 . In addition, emphatic display33 emphasizing the second-floor floor 115 in warehouse 111, which is anobject detected from image G, may be displayed in a superimposed manneron image G displayed in display unit 15. The reason for this is thatwhen the driver sees emphatic displays 31 and 33 displayed on displayunit 15, the driver can recognize a possibility of collision of theupper end of cargo bed 107 with upper frame 113 a and second-floor floor115.

Further, collision possibility determination unit 9 determines thatthere is a danger of collision when the distance between truck 100 andthe object determined to have a possibility of collision with truck 100becomes a predetermined distance or less, and makes the driver of truck100 recognize the danger of collision. Unlike the possibility of thecollision, the danger of collision is a case where there is apossibility of collision with the object unless the driver applies thebrake. Therefore, the predetermined distance is a value obtained bymultiplying the braking distance of the brake by a safe rate. It shouldbe noted that here, the collision means the overlap of the object withthe rectangular range surrounded by guide line 21, or more specifically,the range illustrated with hatching in FIG. 3 . Therefore, in the casewhere height B1 is greater than height B3 of actual cargo bed 107 aswith guide line 21 illustrated in FIG. 4A, the object and cargo bed 107may not be actually collide with each other even when it is determinedthat there is a danger of collision. For example, upper frame 113 a ofentrance 11 and the installation height of second-floor floor 115illustrated in FIG. 4A are higher than height B3 of actual cargo bed107, and therefore it may not actually collide with truck 100 even whenit is determined that the danger of collision.

The specific means for making the driver of truck 100 recognize thedanger of collision is the same as the means for making the driverrecognize the possibility of collision. In this manner, the danger ofcollision can be avoided by making the driver recognize the danger ofcollision when the distance from the object with the possibility ofcollision becomes close to the predetermined distance.

Such a configuration of making the driver of truck 100 recognize thepossibility and danger of collision is especially effective in the casewhere a plan view around the truck 100 also called perspective view asillustrated in of FIG. 4B is displayed on the display unit illustratedin FIG. 2 . Even when the driver sees the plan view illustrated in FIG.4B, second-floor floor 115 and upper frame 113 a of entrance 113 are notdisplayed although warehouse 111 is displayed. As such, the possibilityof collision of truck 100 with upper frame 113 a and second-floor floor115 cannot be determined although it can be determined that there iswarehouse 111 is located on the rear side of truck 100. In this manner,in the case where the plan view is displayed on the display unit 15illustrated in FIG. 2 , rearward monitoring system 1 can make the driverrecognize the possibility of truck 100 with collision of upper frame 113a and second-floor floor 115 with an alarm issued from speaker 17 andthe like. In this manner, the driver can take an action for avoiding thecollision by visually recognizing upper frame 113 a and second-floorfloor 115 by changing the display image of display unit 15 from the planview to an image that shows upper frame 113 a and second-floor floor 115such as the wide-angle image illustrated in FIG. 5 , and the like.

Thus, in the case where the image displayed on display unit 15 does notshow the rear side and upper side of truck 100, rearward monitoringsystem 1 may make the driver recognize a possibility and danger ofcollision when object detection unit 3 detects the object, objectspecifying unit 7 specifies the position, size and velocity vector theobject, collision possibility determination unit 9 determines thepossibility and danger of collision, and there is a possibility anddanger of collision. The image displayed on display unit 15 does notshow the rear side and upper side of truck 100 is a case where a planview around the truck 100 is displayed on display unit 15, and a casewhere a captured image of the range around truck 100 not including therear side and upper side of truck 100 is displayed on display unit 15.Whether the displayed image is a captured image of the range notincluding the rear side and upper side of truck 100 may be determinedbased on the field angle of the camera that has captured the image.

Note that in the case where object specifying unit 7 is a wide-anglecamera, the configuration of generating the plan view may be aconfiguration in which camera images captured by a plurality of camerassuch as object detection unit 3 are converted into a plan view by objectspecifying unit 7 or other computers through a publicly known imageprocessing technique.

In the case where the image displayed on display unit 15 does not showthe rear side and upper side of truck 100, and it is determined thatthere is a possibility of collision of truck 100 with the detectedobject, rearward monitoring system 1 can make the driver of truck 100recognize the possibility of the collision through the following threemeans, for example.

A first example may be a means for making the driver of truck 100recognize the possibility of the collision in which, in the case wherethe image displayed on display unit does not show the rear side andupper side of truck 100 and collision possibility determination unit 9determines that there is a possibility of collision of truck 100 withthe object detected by object detection unit 3, collision possibilitydetermination unit 9 switches the display of display unit 15 from theimage that does not show the rear side and upper side of truck 100 tothe camera image in which the detected object is captured. For example,it is assumed that in the case where display unit 15 shows a plan viewof warehouse 111 illustrated in FIG. 4B, collision possibilitydetermination unit 9 determines that there is a possibility of collisionof truck 100 with second-floor floor 115 and upper frame 113 a ofwarehouse 111. In this case, upper frame 113 a and second-floor floor115 are not displayed in display unit 15, collision possibilitydetermination unit 9 switches the display of display unit 15 from theplan view illustrated in FIG. 4B to image G in which upper frame 113 aand second-floor floor 115 are captured as illustrated in FIG. 5 . Thismeans is advantageous in that the display can be automatically switchedto the image including the object determined to have a possibility ofcollision without the need of the switching of the display image ofdisplay unit 15 by the driver.

Another example may be a means in which in the case where display unit15 is an apparatus of displaying a plan view around the truck 100 andcollision possibility determination unit 9 determines that there is apossibility of collision of truck 100 with the object detected by objectdetection unit 3, collision possibility determination unit 9 draws ondisplay unit 15 a projection line of the position of the detected objectprojected to the plan view to make the driver of truck 100 recognize thepossibility of the collision. For example, as illustrated in FIG. 4B, inthe case where display unit 15 shows a plan view of warehouse 111 andcollision possibility determination unit 9 determines that there is apossibility of collision of truck 100 with second-floor floor 115 andupper frame 113 a of warehouse 111, it suffices that collisionpossibility determination unit 9 draws on display unit 15 projectionline 69 projecting upper frame 113 a on the plan view and projectionline 67 projecting second-floor floor 115 on the plan view in asuperimposed manner on the plan view. This means is advantageous in thatthe driver can determine the plan position of the object with apossibility of collision with truck 100 while displaying the plan view.

Another example may be a means in which in the case where the imagedisplayed on display unit 15 does not show the rear side and upper sideof truck 100, and collision possibility determination unit 9 determinesthat there is a possibility of collision of truck 100 with the objectdetected by object detection unit 3, collision possibility determinationunit 9 displays the camera image in which the object detected by objectdetection unit 3 is captured in a part of the region on display unit 15in a superimposed manner on the image that does not show the rear sideand upper side of truck 100 to make the driver of truck 100 recognizethe possibility of the collision. For example, in the case where displayunit 15 shows a plan view of warehouse 111 illustrated in FIG. 4B andcollision possibility determination unit 9 determines that there is apossibility of collision of truck 100 with second-floor floor 115 andupper frame 113 a of warehouse 111, collision possibility determinationunit 9 displays image G showing upper frame 113 a and second-floor floor115 as illustrated in FIG. 5 in the lower left part, which is a part ofthe region of display unit 15 in a superimposed manner on the plan viewalready shown in display unit 15 as illustrated in FIG. 4B. This meansis advantageous in that the position and the shape of an object with apossibility of collision with truck 100 can be three-dimensionallyvisually recognized while displaying the plan view. The specificstructure of rearward monitoring system 1 according to the firstembodiment is as described above.

Next, the rearward monitoring method using rearward monitoring system 1according to the first embodiment is briefly described with reference toFIG. 6 . First, object specifying unit 7 illustrated in FIG. 2 issues acommand, to object detection unit 3, for detecting an object locatedbehind and above the upper end of the rear end of cargo bed 107 of truck100. Object detection unit 3 acquires the information required forspecifying the object by capturing the rear side of the vehicle at apredetermined time interval on the basis of the command and the like,and transmits the information to object specifying unit 7 (at S1 in FIG.6 , the object detection step).

Object specifying unit 7 illustrated in FIG. 2 specifies the position,size and velocity vector of the object from the information required forspecifying the object, i.e., here, the image obtained by capturing therear side of the vehicle through image analysis and the like (at S2 inFIG. 6 , the object specifying step). Object specifying unit 7 transmitsthe specified position, size and velocity vector of the object tocollision possibility determination unit 9.

Next, collision possibility determination unit 9 illustrated in FIG. 2determines whether there is a possibility of collision with truck 100from the received position, size and velocity vector of the objectobject. When it is determined that there is a possibility of collision,the process proceeds to S4, whereas when it is determined that there isno possibility of collision, the process returns (at S3 in FIG. 6 ).

When it is determined that there is a possibility of collision of truck100 with the object at S3, collision possibility determination unit 9illustrated in FIG. 2 makes the driver recognize the possibility ofcollision by using display unit 15 and speaker 17 installed in cab 105,and the process proceeds to S5 (at S4 in FIG. 6 ). Note that S3 and S4are also referred to as collision possibility determination step.

Next, collision possibility determination unit 9 illustrated in FIG. 2determines whether there is a danger of collision with truck 100 for theobject that is determined at S3 to have a possibility of collision withtruck 100. When it is determined that there is a danger of collision,the process proceeds to S6, whereas when it is determined that there isno danger of collision, the process returns (at S5 in FIG. 6 ). Morespecifically, collision possibility determination unit 9 illustrated inFIG. 2 determines that there is a danger of collision when the objectdetermined to have a possibility of collision with truck 100 and theshortest distance of truck 100 becomes equal to or smaller than apredetermined distance on the basis of the position of the objectspecified at S2.

When it is determined at S5 that there is a danger of collision of truck100 with the object, collision possibility determination unit 9illustrated in FIG. 2 makes the driver recognize the danger of collisionby using display unit 15 and speaker 17 installed in cab 105, andreturns the process (at S6 in FIG. 6 ). Note that S5 and S6 are alsoreferred to as the danger of collision determination step. The above isa brief description of the rearward monitoring method according to thefirst embodiment using rearward monitoring system 1.

As described above, according to the first embodiment, rearwardmonitoring system 1 includes object detection unit 3, object specifyingunit 7, and collision possibility determination unit 9. In thisconfiguration, the object behind and above the upper end of the rear endof truck 100 is detected by object detection unit 3, the detectedposition, size and velocity vector of the object is specified by objectspecifying unit 7, and the possibility of collision of truck 100 withthe detected object is determined by collision possibility determinationunit 9. Thus, the driver can determine the possibility of collision ofthe vehicle with the structure located behind and above the vehicle.

Next, a second embodiment is described with reference to FIGS. 7 to 9 .In the second embodiment, as object detection unit 3, cameras areprovided at two locations at different heights, the rear side and upperside of truck 100 are captured, and each captured image is convertedinto a bird's-eye view as viewed upward from road surface 109, and theobject is specified from the difference of bird's-eye views 64. Notethat in the second embodiment, the components with the same function asthose of the second embodiment will be denoted with the same referencenumerals, and differences from the first embodiment will be mainlydescribed.

As illustrated in FIG. 7 , rearward monitoring system 1 a according tothe second embodiment includes upper camera 3 a and lower camera 3 b asobject detection unit 3. Upper camera 3 a is an image monocular camerathat is installed at the upper end of the rear end of cargo bed 107 oftruck 100, and repeatedly captures at a predetermined time interval theimage of the rear side of truck 100 including the upper side of thehorizontal direction at the installed position. Upper camera 3 a has thesame structure and installation position as the case where objectdetection unit 3 is a monocular camera in the first embodiment.

Lower camera 3 b is a monocular camera that repeatedly captures at apredetermined time interval the image of behind and above the upper endof the rear end of truck 100 including the upper side of the installedposition of upper camera 3 a. Lower camera 3 b is installed at aposition lower than upper camera 3 a at the rear end of truck 100, andin this case installed at the rear end of chassis 103. The installationposition of lower camera 3 b in the vehicle width direction is the sameas that of upper camera 3 a. The structure of lower camera 3 b is thesame as the structure of upper camera 3 a, and is set with a field angleand optical axis that can capture the image of behind and above theupper end of the rear end of truck 100 including the upper side of theinstalled position of upper camera 3 a. In this configuration, rearwardmonitoring system 1 a captures the rear and upper sides of the upper endof the rear end of truck 100 at a predetermined time interval with twocameras, upper camera 3 a and lower camera 3 b. The procedure ofspecifying the position, size and velocity vector of the object locatedbehind and above the upper end of the rear end of truck 100 in thisconfiguration is as follows.

For example, as illustrated in FIG. 7 , it is assumed that pole 41 isprovided to protrude downward from the bottom surface of second-floorfloor 115 of warehouse 111. It is assumed that pole 41 is located behindand above the upper end of the rear end of truck 100. To specify theposition, size, and velocity vector of this pole 41, first, the imageincluding the rear and upper sides of the upper end of the rear end oftruck 100 is captured as in the first embodiment with the two cameras,upper camera 3 a and lower camera 3 b. FIG. 8A schematically illustratesupper camera image G1, which is an image captured with upper camera 3 a.FIG. 8B schematically illustrates lower camera image G2, which is animage captured with lower camera 3 b.

As illustrated in FIGS. 8A and 8B, upper camera image G1 and lowercamera image G2 show at least pole 41. It should be noted that the rearportion of pole 41 is not shown by being hidden by pole 41. In addition,the size of the portion hidden on the rear side is larger in uppercamera image G1 than in lower camera image G2, because upper cameraimage G1 is an image captured at a position closer to pole 41 than lowercamera image G2.

Next, object specifying unit 7 converts upper camera image G1 and lowercamera image G2, which are images captured with upper camera 3 a andlower camera 3 b, into upper bird's-eye view T1 and lower bird's-eyeview T2, which are upward images as viewed from road surface 109. Itsuffices that the virtual view points of upper bird's-eye view T1 andlower bird's-eye view T2 are set to the center of the projected range ofthe case where the capturing ranges of upper camera image G1 and lowercamera image G2 are projected on road surface 109. FIG. 9A schematicallyillustrates upper bird's-eye view T1 converted from upper camera imageG1. FIG. 9B schematically illustrates lower bird's-eye view T2, which isan image captured with lower camera 3 b.

As illustrated in FIGS. 9A and 9B, an object with a height such as pole41 is largely differ in the shapes shown in upper bird's-eye view T1 andlower bird's-eye view T2 and the actual shape. In addition, bycomparison between upper bird's-eye view T1 and lower bird's-eye viewT2, the displayed shapes and sizes are largely different from eachother. More specifically, the rear side of the portion that is unshownby being hidden by pole 41 in upper camera image G1 and lower cameraimage G2 is image-corrected into the same one as pole 41. Pole 41 islocated at approximately the center in the vehicle width direction oftruck 100, and the rear side of the portion that is unshown by beinghidden by pole 41 in upper camera image G1 and lower camera image G2 isimage-corrected into trapezoidal corrected part 65.

In addition, upper bird's-eye view T1 has a larger corrected part 65than in lower bird's-eye view T2. The reason for this is that in uppercamera image G1, the portion hidden in rear of pole 41 is larger than inlower camera image G2. The position and size of difference 64 ofcorrected part 65 are correlated with the position and size of pole 41.More specifically, the position of difference 64 is on the rear side ofthe position of pole 41, the position of pole 41 can be specified fromthe position of difference 64. When the position can be specified, thedistance D between pole 41 and the rear end of cargo bed 107 can bedetermined. In addition, since difference 64 increases as the size ofpole 41 increases, the vertical height of pole 41 can be specified fromlength ΔL of difference 64 in the front-rear direction of truck 100.Further, the width of pole 41 can be specified from the width ofdifference 64 in the vehicle width direction of truck 100, which isshortest width μW in FIG. 9A. In addition, since area ΔS of difference64 increases as the length of pole 41 in the Z direction and the widthin the Y direction thereof increase, the length and width of pole 41 canbe estimated from area ΔS of difference 64. Therefore, the position andsize of the object located behind and above the upper end of the rearend of truck 100 can be specified from the position and size ofdifference 64.

In addition, in the case where upper camera image G1 and lower cameraimage G2 captured at a predetermined interval are sequentially convertedinto upper bird's-eye view T1 and lower bird's-eye view T2, the velocityvector can be determined from the variation of the size and position ofdifference 64. More specifically, in the case where the size ofdifference 64 is gradually increased with time, the direction of therelative speed of the object with respect to truck 100 is the directionapproaching truck 100. In addition, the larger the variation of the sizeof difference 64 per unit time, the larger the relative speed of theobject with respect to truck 100.

Therefore, the velocity vector of the object located behind and abovethe upper end of the rear end of truck 100 can be specified from thevariation of the position and size of difference 64. In this manner,there is correlations between the position, size, and variation thereofof difference 64, and the position, size, and velocity vector of pole41. Therefore, the position, size, and velocity vector of pole 41 can bedetermined by determining the correlations through experiment and thelike, and applying difference 64 to the determined correlations. Notethat the configurations other than the means for specifying the objectin the second embodiment, e.g., the criterion for determining apossibility and danger of collision, are the same as those of the firstembodiment, and the description thereof is omitted.

The first embodiment and the second embodiment may be selected asnecessary in consideration of the advantage. For example, the firstembodiment is advantageous in that the number of the installationpositions of object detection unit 3 is smaller than in the secondembodiment because object detection unit 3 need only be installed at theupper end of the rear end of cargo bed 107. The second embodiment isadvantageous in that the position and size of the object can be detectedwith high accuracy even with a monocular camera as object detection unit3.

The above description of the present disclosure is based on theembodiments, but the present disclosure is not limited to theembodiments. It is natural for those skilled in the art to come up withvarious variations and improvements within the scope of the technicalconcept of the present disclosure, and these are naturally included inthe present disclosure.

1. A vehicle rearward monitoring system configured to monitor an objectlocated behind and above a vehicle, the vehicle rearward monitoringsystem comprising: an object detection unit installed in the vehicle andconfigured to detect the object located behind and above an upper end ofa rear end of the vehicle; an object specifying unit configured tospecify a position, a size and a velocity vector with respect to thevehicle of the object detected by the object detection unit; and acollision possibility determination unit configured to determine apossibility of collision of the vehicle with the object detected by theobject detection unit from the position, the size and the velocityvector of the object specified by the object specifying unit, and make adriver of the vehicle recognize the possibility of collision when it isdetermined that there is the possibility of collision.
 2. The vehiclerearward monitoring system according to claim 1, wherein the objectdetection unit is an upper camera installed at the upper end of the rearend of the vehicle and configured to repeatedly capture at apredetermined time interval an image of a rear side of the vehicleincluding an upper side of an installed position; and wherein the objectspecifying unit specifies a position of the object from the imagecaptured by the upper camera through edge extraction, specifies the sizeof the object from a range occupied by the object in the image, andcalculates the velocity vector from a variation of the position of theobject in a plurality of images captured at the predetermined timeinterval, and a variation of the range occupied by the object in theimage.
 3. The vehicle rearward monitoring system according to claim 1,wherein the object detection unit is a clearance sonar installed at theupper end of the rear end of the vehicle, and configured to emitultrasound to surroundings and detect returning ultrasound reflected bythe object; and wherein the object specifying unit specifies theposition, the size and the velocity vector of the object from a timefrom emission to detection and a returning direction of the returningultrasound reflected by the object that is detected by the clearancesonar.
 4. The vehicle rearward monitoring system according to claim 1,wherein the object detection unit includes: an upper camera installed atthe upper end of the rear end of the vehicle, and configured torepeatedly capture at a predetermined time interval an image of a rearside of the vehicle including an upper side of a horizontal direction atan installed position, and a lower camera installed at a position lowerthan the upper camera at the rear end of the vehicle, and configured torepeatedly capture at a predetermined time interval an image of the rearside of the vehicle including the upper side of the installed positionof the upper camera, and wherein the object specifying unit convertsimages captured at the predetermined time interval by the upper cameraand the lower camera into bird's-eye views that are upward images asviewed upward from a road surface, and, in the bird's-eye view of theimage captured by the upper camera and the bird's-eye view of the imagecaptured by the lower camera, the object specifying unit specifies theposition, the size and the velocity vector of the object from adifference of an unshown portion that is hidden by the object in theimages captured by the upper camera and the lower camera.
 5. The vehiclerearward monitoring system according to claim 1, wherein the collisionpossibility determination unit determines that there is a possibility ofcollision and makes the driver of the vehicle recognize the possibilityof collision in a case where: the size of the object specified by theobject specifying unit is equal to or greater than a predetermined size,the object specified by the object specifying unit falls within a regionthat is surrounded by a guide line representing an outer periphery ofthe rear end of the vehicle when the guide line is extended rearward ofthe vehicle, the velocity vector of the object specified by the objectspecifying unit is equal to or greater than a speed of the vehicle, anddirections of the object and the vehicle velocity vector are opposite toeach other.
 6. The vehicle rearward monitoring system according to claim1, wherein when a distance between the vehicle and the object determinedto have a possibility of collision with the vehicle becomes equal to orsmaller than a predetermined distance, the collision possibilitydetermination unit determines that there is a danger of collision andmakes the driver of the vehicle recognize the danger of collision. 7.The vehicle rearward monitoring system according to claim 1, whereinwhen a plan view of a periphery of the vehicle, or an image in which arange not including a rear side and an upper side of the vehicle of theperiphery of the vehicle is captured is displayed on a display unitprovided in a cab of the vehicle, the object detection unit detects theobject, the object specifying unit specifies the position, the size andthe velocity vector of the object, and it is determined that there is apossibility of collision by the collision possibility determination unitthrough determination of a possibility of collision, the driver of thevehicle is made recognize the possibility of collision.
 8. The vehiclerearward monitoring system according to claim 7, wherein when it isdetermined that there is a possibility of collision of the vehicle withthe object detected by the object detection unit, the collisionpossibility determination unit makes the driver of the vehicle recognizethe possibility of collision by switching a display of the display unitto a camera image in which the object detected is captured, from theplan view, or the image in which the range not including the rear sideand the upper side of the vehicle of the periphery of the vehicle iscaptured.
 9. The vehicle rearward monitoring system according to claim7, wherein the display unit is an apparatus configured to display theplan view of the periphery of the vehicle; and wherein when it isdetermined that there is a possibility of collision of the vehicle withthe object detected by the object detection unit, the collisionpossibility determination unit makes the driver of the vehicle recognizethe possibility of collision by drawing a projection line on the displayunit in a superimposed manner on the plan view, the projection linebeing obtained by projecting onto the plan view the position of theobject detected.
 10. The rearward monitoring system according to claim7, wherein when it is determined that there is a possibility ofcollision of the vehicle with the object detected by the objectdetection unit, the collision possibility determination unit makes thedriver of the vehicle recognize the possibility of collision bydisplaying a camera image in which the object detected is captured in apart of a region of the display unit in a superimposed manner on theplan view, or the image in which the range not including the rear sideand the upper side of the vehicle of the periphery of the vehicle iscaptured.
 11. A vehicle rearward monitoring method configured to monitoran object located behind and above a vehicle, the vehicle rearwardmonitoring method comprising: detecting the object located behind andabove an upper end of a rear end of the vehicle; specifying a position,a size and a velocity vector with respect to the vehicle of the objectdetected by the detecting; and determining a possibility of collision ofthe vehicle with the object detected by the detecting from the position,the size and the velocity vector of the object specified by thespecifying, and making a driver of the vehicle recognize the possibilityof collision when it is determined that there is the possibility ofcollision.